Lubricant additives for oxidation inhibition and rust inhibition

ABSTRACT

NEW COMPOSITIONS OF MATTER ARE PROVIDED WHICH ARE USEFUL AS ADDITIVES IN LUBRICANTS AND WHICH ARE OXIDATIVELY AUTOINHIBITIVE AND/OR RUST-INHIBITIVE, THE COMPOSITIONS COMPRISING SUBSTITUTED PHENYLALKANES OR HYDROXYARYLSTEARIC ACIDS OR SALTS THEREOF WHEREIN THE ARYL GROUPS ARE ATTACHED TO THE ALKYL CHAIN AT A TERTIARY CARBON ATOM.

United States Patent 3,573,333 LUBRICANT ADDITIVES FOR OXIDATION INHIBITION AND RUST INHIBITION Jonathan L. Snead, Philadelphia, Joseph F. Messina,

Havertown, and Henry Gisser, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Continuation of application Ser. No.

613,077, Jan. 30, 1967. This application Aug. 19,

1969, Ser. No. 853,600

Int. Cl. C08h 17/36 US. Cl. 260-413 1 Claim ABSTRACT OF THE DISCLOSURE New compositions of matter are provided which are useful as additives in lubricants and which are oxidatively autoinhibitive and/or rust-inhibitive, the compositions comprising substituted phenylalkanes or hydroxyarylstearic acids or salts thereof wherein the aryl groups are attached to the alkyl chain at a tertiary carbon atom.

This application is a continuation of application 'Ser. No. 613,077, filed Jan. 30, 1967, now abandoned.

This invention relates to compounds useful as lubricant additives and more particularly concerns compounds which are oxidatively autoinhibitive and/or rust inhibitive.

Diesters and hydrocarbons are widely used as lubricants for such mechanisms as jet engines and hydraulic systems. These organic fluids are subject to oxidation, with consequent deterioration in physical and chemical properties. The addition of inhibitors is only a partial solution to the oxidation problem, in that the effects are short-lived unless sufficiently high concentrations are added, in which case, however, the other properties of the fluid, such as viscosity and liquid range, may be undesirably altered.

In the oxidation of hydrocarbons, for example, oxidation will occur preferentially at a tertiary CH bond and the same is true of saturated aliphatic diesters. In general, the order of increasing resistance to oxidative attack a CH bonds is tertiary, secondary, and primary. This is to be expected from the free radical nature of the oxidation process and the fact that the relative probability of attack of alkyl radicals at CH bonds decreases in the order aforementioned.

These theoretical principles have been utilized in our invention to produce compounds that generate oxidation inhibitors, More specifically, selected aromatic groups have been attached to tertiary CH bonds of hydrocarbons by synthesis. These compounds when subjected to oxidation, form hydroperoxides which break down to yield phenols, the active antioxidants. The phenols thus generated are capable of slowing down further oxidation of the remaining substrate (original compound) or other substrates which are less stable to oxidation.

Another aspect of the invention involves incorporating select groups on the tertiary CH bond of long-chain fatty acids and fatty acid salts (soaps) to produce compounds which possess combined oxidation and rust inhibitory properties. The long hydrocarbon chain terminated by the strongly polar acid (or salt) group is an effective rust inhibitor. At the same time, the phenolic side chain, effective in preventing rapid oxidation, when oxidized, forms hydroperoxides that break down to yield other phenols more effective as antioxidants than the original compound.

It is therefore an object of this invention to provide improved lubricant additives which impart good oxidation stability to the lubricant.

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Another object of the invention is to provide improved lubricant additives which impart good rust-inhibitive properties to the lubricant.

Still another object of the invention is to provide an additive to lubricant fluids which yields both good oxidation stability and good rust-inhibitive properties, said additive comprising but a single molecule.

Other and further objects of the invention will be apparent to those skilled in the art upon study of this disclosure.

Now in accordance with our present invention, the inhibitor-generating hydrocarbon above described will be an electron-donating, substituted phenylalkane wherein the ring is attached to the alkyl group at a tertiary carbon atom. The following compounds are examples of the type of structures involved:

OCHa

When the compounds with the above molecular structures are added to oxidatively unstable compounds, the oxidation rates of the latter are decreased or completely inhibited, as illustrated by the data below:

TABLE 1.OXIDATION RATES OF MIXTURES OF SEC- BUTYLBENZENE AND INHIBITOR-GENERATING HY- DROCARBONS AT 100 C.

Mole, Time, Inhibitor additive percent Rate 1 hours None 0 7. 2 5-10 4-sec-butyl-4-methoxybipheuyl.- 6. 8 1. 4 5-10 4-sec-butylbiphenyl 7. 4 5.0 5-10 1 Moles 02/111018 compound per hour X10 As an example, the inhibitor-generating compound 4- sec-butyl-4'-methoxybiphenyl may be prepared as follows:

p-Phenylanisole (46 g.; 0.25 mole) in 700 ml. of hot heptane was placed in a one-liter four-necked flask, fitted With a stirrer, reflux, dropping funnel, and a thermometer. Anhydrous AlC13 (13.3 g.; 0.1 mole) was added and the temperature maintained at -85 C. with the addition of chlorobutane (25 g.; 0.27 mole) over a period of 2.5 hours, with stirring. Stirring and heating at 75-85 C. was continued for 5.5 hours or until evolution of hydrogen chloride had ceased. The reaction mixture was poured over an equivalent amount (by voltune) of crushed ice, with vigorous stirring, to hydrolyze the com lex. The organic layer was washed free of acid with distilled water; dried over anhydrous Na SO filtered, and the heptane removed under reduced pressure. The unreacted solid pphenylanisole Was distilled, in vacuo, using a steamjacketed condenser. The residue was distilled in a pot still at 15-20 microns pressure. The liquid distillate was then fractionated through a short Vigreux column to yield 4- sec-butyl-4'-methoxybiphenyl, B.P. 137 C. at 0.65 mm.

Oxidation stability of the mixtures of unstable compounds and inhibitor additives was determined at C. by using standard Warburg manometry as described by Umbreit, Burria, and Stauffer, Manometric Techniques, pp. 1-17, 46-7, 77-8, Burgess Publishing Co., Minneapolis, Minn., 1959. One milliliter of compound was introduced into the main compartment of the Warburg flask. Since oxygen consumption in the initial stages of autoxidation was measured, it was not necessary to use absorbents for volatiles. The flask was immersed in a 100 C. oil

4 bath and allowed to come to equilibrium, during which until after the induction period and a considerable intime the system was flushed with oxygen for approximatecrease in acidiy and viscosity was obtained. The results ly 15 minutes. When the system was finally closed to the are presented in Table II below:

TABLE II.OXIDATION F ARYLSIEARIC ACIDS IN BIS(2-ETHYLHEXYL) SEBACAIEI Neutralization number increase, Eq. mg. Viscosity increase, percent at KOH/g. oil, hours 3 8 C., hours Induction 240 at period, Additive 24 48 72 06 168 150 336 24 48 72 90 168 240 336 hours None 23 75.0 W01" l0)-(2-hydroxy-5-tert-butylphenyl)stearic acid 0.1 37 0(or 10)-(2,3-dihydroxyphenyl)stearic acid 0.2 02 9(01' 10)-(2-hydroxy-3-isopropyl-fi-methylphenyl)stearic acid 0. 1 38 9,12-Bis(4-hydroxyphenyl)stearic acid 0.2 240 Calcium 9(or 10)-p-hydroxyphenyl stearat 0 70 Barium 9 (or 10)phydroxyphenyl stearate 0.3 56 Strontium 0 (or 10)-p-hydroxyphenyl stearate 0.2 81

None- 4 0(or l0)-(2,3-dihydroxyphenyl)stearic acid 26 9,12-Bis(4-hydroxyphenyDstearic acid 33 Barium 9(01' 10)-p-hydroxyphenyl stearate 28 1 Two percent of the inhibitor in solution unless otherwise indicated. 2 Determined in accordance With ASIM D66454. 3 Determined in accordance with ASTMD445-53T.

atmosphere, excess oxygen pressure was bled off so that The general effectiveness of a particular additive as an 0.1 to 0.5 cm. of pressure remained. Oxygen consumption antioxidant may rapidly be determined from Table II was calculated as moles of oxygen per mole of compound. above by noting the duration of the induction period.

The inhibitor-generating long-chain fatty acids. (and That is, the longer the induction period, generally, the salts) of our invention will be hydroxyarylstearic acids 0 more effective the antioxidant. Although all of the hywherein the aryl group is attached to the long acid chain, droxyarylstearie acids were effective to some extent as at various points, through a tertiary carbon. Examples of antioxidants, excellent results were obtained through the the type of structures involved are given below: use of 9 (or 10)-(2,3-dihydroxyphenyl) stearic; 9,12-bis Q( 2) HZ)n'COOH CH3(CHZ),.OH(CH2)D.COOH (4-hydroxyphenyl) stearic acids; and the alkaline earth I 35 salts of 9 (or 10)-p-hydroxyphenylstearic acid. OH OH Rust inhibition data were obtained with the use of a cyclic humidity cabinet wherein test specimens were continuously exposed to alternating cycles of 4 hours at 43.3 C. and 80% relative humidity, followed by 4 hours at where n+n=15 where n+n=15 4O 544 C. and 95% relative humidity. These conditions R=iso-Propy1 are considered severe and give rise to one period of con- RECHS trolled condensation during each S-hour cycle. Rust inhibition results are presented in Table III below: omom)nomonmcmcnnn'coon [CH3(CHz)uCH(CH2)u'COO]2X l l I TABLE III Humidity Cabinet Rust Test Data 1 Additive: Hours to failure None 24 OH OH OH Oleic acid 84 where u+n=12 where n+n=15 Linoleic acid 72 X=ca1ciumstrontium 9 (or 10)-(2-hydroxy-5-tert-butylphenyl)stearic or Barium id 9 The above have been found to be compounds effective 9 (or 10)-(2,3-dihydroxyphenyl)stearic acid 132 in inhibiting both oxidation and rust when used in instru- 9 (or 10)-(2-hydroxy-3-isopro yl-6-methylphenment lubricant compositions. The long hydrocarbon chain yDstearic acid 96 terminated by the strongly polar acid (or salt) group, ad- 9,12-bis(4-hydroxyphenyl)stearic acid 128 heres to the metal to be lubricated to form a monomolec- Calcium 9 (or 10)-p-hydroxyphenyl stearate 162 ular layer which prevents rust formation. In addition, hy- Barium 9 (or l0)-p-hydroxyphenyl stearate 186 droxyarylstearic acids (or salts) are effective as antioxi- Strontium 9 (or l0)-p-hydroxyphnyl stearate 132 dams because of formation of an inhibitor Via autoxida 1 Bis (Z-ethylhexyl) sebacate containing 2% of the additive. tion at the tertiary carbon atom.

In order to determine oxidation stability of the generic F m th data pres nted above, it can be seen that most group f Compounds bo ti d t diff r nt temperaof the compounds exhibit protection against rust. Since tures a dynamic test was employed which is similar to 9 (or 10)-2,3-dihydroxyphenyl) stearic; 9,12-bis(4-hyth t d ib d i th F d l S ifi tio f L b i. droxyphenyl)stearic acids; and the alkaline earth salts of cants, Liquid Fuels, and Related Products; Methods of 9 (01 10)-p-hydroxyphenylstearic acid provide better pro- Inspection, Sampling, and Testing VV-L-79le, May 21, tection than the more highly substituted compounds, it 1953, Method 5308.3 entitled Corrosiveness and Oxida- W uld appear that the bulky alkyl groups may prevent tion Stability of Light Oils. Two weight percent solutions close alignment of the molecules in the absorbed monoof the additive compounds in bis(2-ethylhexyl) sebaeate, layer or decrease the lateral attractions (Van der Waals a typical diester lubricant, were oxidized at forces).

and C. in the presence of copper and steel catalyst Our combination oxidation and rust inhibitor comstrips (1.750 x 0.735 x 0.025 inches). Samples of 10 ml. pounds were prepared as described below, using 9 (or 10)- were withdrawn periodically for viscosity and neutralizap-hydroxyphenylstearic acid, and barium 9 (or 10)-p-hy tion number determinations, and the test was continued 7 5 droxyphenyl stearate as examples.

Isomeric arylstearic acids: The 9 (or 10)-arylstearic acids were prepared by the Friedel-Crafts condensation of oleic acid with phenols in the presence of equimolar quantities of anhydrous aluminum chloride. Phenol (7 parts) was mixed with 99% purity oleic acid (1 part) and anhydrous aluminum chloride (1.3 parts) was gradually added with stirring. After the vigorous reaction had subsided, the mixture was heated to 80 C. for 68 hours or until the evolution of HCl fumes ceased. The reaction mixture was poured into 20% hydrochloric acid and the organic layer extracted with ethyl ether. The ether extract was washed with water until acid-free and dried over anhydrous Na SO After filtration, the ether was removed by distillation at atmosphere pressure. Excess phenol was then removed by distillation, in vacuo, until the pot temperature of 150 C. :at 1 mm. was obtained. The residue, on distillation from a short-path molecular still at 5-10 microns pressure, yielded 9 (or 10)-p-hydroxyphenylstearic acid. The 9,12-diarylstearic acid was prepared in a similar manner by reaction of linoleic acid with phenol.

The alkaline earth salts of 9 (or 10)-p-hydroxyphenyl) stearic acid were prepared by conversion of the sodium salt. To a benzene solution of the sodium salt (2 parts) prepared from the free acid and NaOH in a 1:1 ratio was added, dropwise, with stirring, aqueous barium chloride (1 part). The reaction mixture was refluxed for one-half hour, cooled, and poured into a separatory funnel. The product was washed free of chloride and then transferred to a clean flask and the remaining Water was removed as References Cited UNITED STATES PATENTS 3,468,920 9/1969 Larimer et al. 260-407 OTHER REFERENCES Snead et al.: I & EC Product Research and Development, vol. 5, No. 3, September 1966, pp. 222-225.

LEWIS GOTTS, Primary Examiner E. G. LOVE, Assistant Examiner US. Cl. X.R. 

